InterPro domain: IPR039418

Peptidase S24 LexA-like proteins are involved in the SOS response leading to the repair of single-stranded DNA within the bacterial cell [ 1 ]. Proteins containing this domain includes LexA, MucA and UmuD. LexA ( 3.4.21.88 ) is the repressor of genes in the cellular SOS response to DNA damage [ 2 ].

The LexA-like proteins contain two-domains: an N-terminal DNA binding domain and a C-terminal domain (CTD) that provides LexA dimerization as well as cleavage activity [ 3 ]. They undergo autolysis, cleaving at an Ala-Gly or a Cys-Gly bond, separating the DNA-binding domain from the rest of the protein [ 4 ].

The LexA, UmuD and MucD proteins interact with RecA, which activates self cleavage either derepressing transcription in the case of LexA [ 5 ] or activating the lesion-bypass polymerase in the case of UmuD and MucA. UmuD'2, is the homodimeric component of DNA pol V, which is produced from UmuD by RecA-facilitated self-cleavage. The first 24 N-terminal residues of UmuD are removed; UmuD'2 is a DNA lesion bypass polymerase [ 6 , 6 ]. MucA [ 7 , 8 ], like UmuD, is a plasmid encoded a DNA polymerase (pol RI) which is converted into the active lesion-bypass polymerase by a self-cleavage reaction involving RecA [ 9 ].

1. Aeons of distress: an evolutionary perspective on the bacterial SOS response. FEMS Microbiol. Rev. 31, 637-56
2. Interaction of Escherichia coli RecA protein with LexA repressor. II. Inhibition of DNA strand exchange by the uncleavable LexA S119A repressor argues that recombination and SOS induction are competitive processes. J. Biol. Chem. 271, 23874-83
3. Crystal structure of LexA: a conformational switch for regulation of self-cleavage. Cell 106, 585-94
4. Cleavage of LexA repressor. Meth. Enzymol. 244, 266-84
5. Analysis of Escherichia coli RecA interactions with LexA, lambda CI, and UmuD by site-directed mutagenesis of recA. J. Bacteriol. 182, 1659-70
6. Converting a DNA damage checkpoint effector (UmuD2C) into a lesion bypass polymerase (UmuD'2C). EMBO J. 20, 4287-98
7. Intermolecular cleavage by UmuD-like enzymes: identification of residues required for cleavage and substrate specificity. J. Mol. Biol. 285, 2199-209
8. Plasmid-encoded MucB protein is a DNA polymerase (pol RI) specialized for lesion bypass in the presence of MucA', RecA, and SSB. Proc. Natl. Acad. Sci. U.S.A. 97, 11227-31
9. Genetic and biochemical characterization of a novel umuD mutation: insights into a mechanism for UmuD self-cleavage. J. Bacteriol. 183, 347-57